Game suddenly decides to crash?

I just recently started playing, and I was having fun for two days. I played a few matches this morning, but I lagged a whole lot. I then restarted my computer in hopes that would work, and then when I launched the game, it just says I needed to reinstall.

Fine, whatever, that'll take time out of my day but I guess I can do other stuff. 4 hours later, client thing is done (Why doesnt the downloader just download the new client?) and I try to launch. SAME. THING. HAPPENS.

Any fixes? is this a common problem?